In general, the fundamental steps for processing a color photographic material are a color development step and a desilvering step. In the color development step, the exposed silver halide is reduced by a color developing agent to form silver and at the same time the oxidized color developing agent reacts with color forming agents (couplers) to form dye images. In the subsequent desilvering step, silver formed in the color development step is oxidized by an oxidizing agent called a bleaching agent; this oxidized silver is then dissolved by a complex ion forming agent of silver ions called a fixing agent. As the result of applying the desilvering step, dye images only are formed on the color photographic material.
Usually, after these steps, a wash process removes unnecessary components left on the color photographic material from the processing solutions. In the case of a color photographic paper and a reversal color photographic paper, processing is finished by the above-described steps and then the color photographic material is generally subjected to a drying step. In the case of a color negative photographic film and a color reversal photographic film, however a stabilization step is added to the foregoing steps. It is well-known that formalin (a 37% aqueous solution of formaldehyde) is used in the stabilizing bath to prevent fading of magenta dyes caused by magenta couplers remaining in the color photographic material after processing. A certain amount of the formaldehyde vapor is generated during preparation of the stabilizing bath containing formalin and during drying of color photographic materials processed in these baths.
It is known that the inhalation of formalin is harmful for the human body and the Japan Association of Industrial Health that the allowable concentration of formaldehyde in a working environment is 0.5 ppm or less. Accordingly, efforts to reduce the concentration of formalin in a stabilizing bath and replacing formaldehyde with an alternative have been made to improve the working environment.
As an alternative for formalin, hexamethylenetetramine series compounds are described in JP-A-63-244036 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). By using these compounds, the concentration of formaldehyde, that is, the vapor pressure of formaldehyde can be reduced but the ability to prevent fading of magenta dye is also reduced. Thus, the essential purpose of using these compounds is diminished for when the color images formed are allowed to stand, the magenta color fades within few weeks, even at room temperature.
Also, U.S. Pat. Nos. 4,786,583 and 4,859,574 describe urea and N-methylol compounds such as guanidine, melamine, etc.
Further, JP-A-61-75354, JP-A-61-42660, JP-A-62-255948, JP-A-1-295258, and JP-A-2-54261 describe 1-(dihydroxyaminomethyl)benztriazoles, JP-A-1-230043, etc., describes N-(morpholinomethyl)heterocyclic thiones and N-(piperidinomethyl)heterocyclic thiones, and JP-A-2- 153350 describes bis(alkylamino)methane and bis(anilino)methane.
However, although some these compounds reduce vapor pressure of formaldehyde (as compared with that formed when using formalin alone), the image storage stability is poor. The rest of these compounds that do have improved image storage stability produce a vapor pressure of formaldehyde similar to that produced when using formalin. Thus, the foregoing compounds do not simultaneously improve the image storage stability and reduce of the vapor pressure of formaldehyde.
It has also been found that when these compounds are used in a larger amount than that of formaldehyde for obtaining the improved image storage stability similar to that obtained by formalin, the side reaction is easily generated. Examples of the side reaction include formation of stains, deterioration of the storage stability of other dyes contained in the color photographic material processed as well as yellow dyes and cyan dyes, and attachment to the color photographic material which stains the color images formed.
Thus, there has been strong demand for an innovative process to prevent magenta dye fading and lower the vapor pressure of formaldehyde.